Floatless fluid level gauge

ABSTRACT

A floatless, electrical, fluid level gauge is disclosed in which fluid level indication is derived from the voltage appearing at the center tap of a resistive voltage divider network. The elements of said voltage divider network comprise two volumes of the fluid to be gauged.

United States Patent Harper 51 July 25,1972

[54] FLOATLESS FLUID LEVEL GAUGE [72] Inventor: Patrick D. Harper, 901St. Andrews Way,

Bel Air, Md. 21014 [22] Filed: Feb. 25, 1970 [2]] Appl. No.: 14,132

[52] U.S. Cl. ..73/304 R [51] Int. Cl. ..G01I 23/24 [58] Field of Search..73/3Q4 R; 324/29 [56] References Cited UNITED STATES PATENTS 2,659,06811/1953 Erickson ..73/304 X FOREIGN PATENTS OR APPLICATIONS 242,648 I5/1946 Switzerland ..73/304 'IIIIII'IIIIA 842,554 6/l952 Germany..73/304 OTHER PUBLICATIONS IBM Technical Disclosure Bulletin; PlatingRange Testing by Judge et al.; from Vol. 4, No. 10; Mar. 1962 PrimaryExaminer-Louis R. Prince Assistant Examiner-Denis E. CorrAtwrney-Plante, Arens, Hartz, Smith and Thompson. Bruce L. Lamb andWilliam G. Christoforo 571 ABSTRACT A floatless, electrical, fluid levelgauge is disclosed in which fluid level indication is derived from thevoltage appearing at the center tap of a resistive voltage dividernetwork. The ele ments of said voltage divider network comprise twovolumes of the fluid to be gauged.

20 Claims, 11 Drawing Figures Pmmnted July 25, 1972 2 Sheets-Sheet l w mI I 1 I I I W T a A "1 11 ,!11114 m wllllllllll I I G I FIG. 2

iNVENTOR PATRICK D. HARPER ATTORNEYS Patented July 25, 1972 2Sheets-Shout 2 A, N06 I ATTORNEYS m INVENTOR PATRICK D. HARPER AW,

II C m QE FLOATLESS FLUID LEVEL GAUGE BACKGROUND OF THE INVENTIONFloat-type electrical fluid level gauges, well known in the art forseveral decades, are still by far the most commonly employed automotivefuel gauges. They have not been generally adapted for use as lubricatingoil level gauges because the viscosity of lubricating oils would causethem to interfere with proper operation of the gauge, and becausefloat-type gauges require a greater volume of space for operation thancan be conveniently provided in an automotive crankcase.

Even in fuel gauge applications, the float-type gauges exhibit certaindisadvantages. One disadvantage is a greater tendency to mechanicalfailure than would be exhibited by a gauge without moving parts. Anotheris inaccuracy of output signal resulting from surface waves in the fluidor fluid displacement as a function of vehicle attitude. Moreover, sincethe electrical signal is generated by a wiper arm moving across aresistance element in an atmosphere comprising gasoline vapor and air, ahazard of fire or explosion exists.

In order to overcome these disadvantages with respect to fuel gauges,and other disadvantages particular to other specific applications,various types of floatless fluid level gauges have been developed. Onesuch type is the reactive type in which the electrical reactance of thegauge is made to vary by the presence of the fluid to be gauged at thegauge elements. See, for example, the capacitive gauge of Meyers (U.S.Pat. No. 2,741,124) and the inductive gauge of Mastras (U.S. Pat. No.3,058,345). These gauges have the disadvantage of requiring relativelycomplex and expensive a. c. bridge and source circuits which add expenseand decrease reliability. Another type of floatless gauge is theresistive type. These include thermoresistive gauges such as Talbots(U.S. Pat. No. 2,894,390), in which the fluid cools a thermoresistiveelement whose resistance is therefore proportional to the amount of itsarea covered by fluid. Another example of resistive type floatlessgauges includes gauges in which a resistance element is shorted at apoint corresponding to the level of the fluid to be gauged, by the fluiditself, as in Wright (U.S. Pat. No. 3,003,355) or by a secondary fluid,as in Pleuger (U.S. Pat. No. 2,931,225). A final example comprisesgauges in which the resistance of a volume of the fluid itself ismeasured as in Morris (U.S. Pat. No. 3,285,068).

These floatless gauges all have the disadvantage of being responsive tochanges in the temperature and composition of the fluid to be gauged.This disadvantage has been overcome in the art by the addition ofreference sensors. These, however, require the use of compensatingbridge circuitry which adds cost and decreases reliability.

Against this background, a floatless electrical fluid level gauge wasinvented by M. Slavin which provides fluid level indication independentof the temperature or composition of the fluid to be gauged, without theuse of additional means for compensation. Slavins invention is fullydisclosed in U.S. Pat. No. 3,465,588, assigned to the assignee of thisapplication. Slavin teaches a single continuous resistance elementdepended into the fluid to be gauged, whereby an electric field isproduced in the fluid from its surface to the bottom of its container.The magnitude of the field is proportional to the depth of the fluidbecause the resistance element is continuous. A collector is alsodepended into the fluid and acquires a potential equal to one-half thevalue of the potential of the resistance element at the surface of thefluid. The potential value of the collector results from the balance ofionic currents in the fluid which causes the collector to behave as thecenter tap of a resistive voltage divider having equal resistance anns.The disadvantage of Slavins gauge is that in order to obtain thebalanced voltage divider which Slavin teaches is required, a continuousresistance element is required; this adds substantially to the cost ofproducing the gauge.

This invention relates to a floatless electrical fluid level gauge inwhich fluid level indication is derived from the voltage appearing atthe center tap of a resistive voltage divider network wherein saidvoltage divider network need not be, and typically is not, in balance,and has as an object the production of a floatless electrical fluidlevel gauge which is highly reliable and inexpensive to manufacture.

Another object of the invention is to provide a floatless electricalfluid level gauge which is wholly d. c. operated.

' Another object is to provide such fluid level gauge which is adaptableto a wide range of fluid conductivity.

It is a further object to provide a floatless fluid level gauge which isparticularly adaptable to gauging gasoline levels.

It is also an object of the invention to provide a gauge which will drawless than one microampere of current when used as an automotive gasolinegauge.

Yet another object is to provide a gauge which will provide any desiredgauge function, linear or non-linear, which will indicate the depth orvolume of fluid in a container of arbitrary shape.

These and other objects, features and advantages of the invention willappear from the following description and appended claims when read inview of the accompanying drawings.

Briefly, the invention is embodied in a fluid level gauge comprisingthree conductive elements which are depended into the fluid to begauged. An electrical potential is maintained across a pair of saidelements. One element of said pair of elements is maintained at areference potential which is preferably the ground potential for thesystem in which the gauge is employed. This element will be referred toherein as the reference plane. The other element of said pair ofelements is maintained at some potential above said reference potentialand will be referred to herein as the potential plane. The third saidconductive element is disposed between said pair of elements in one ofthe embodiments disclosed, and adjacent to said pair of elements inanother of the embodiments disclosed. Said third element is referred toherein as the collector. Means are provided whereby the resistance ofthe portion of the fluid to be gauged, electrically appearing betweenthe potential plane and the collector, varies with the depth of fluid ata rate different from the rate at which the resistance of the portion offluid electrically between the collector and the reference elementvaries withthe depth of fluid. Said means comprise alternatively shapingof the potential plane and reference element, or shaping or dispositionof the collector, or the application to a portion of one of said pair ofelements of a non-conductive substance. The collector thereforefunctions as the center tap of a resistor voltage divider networkcomprising the fluid between the potential plane and the collector as afirst resistor, and the fluid between the reference element and thecollector as a second resistor. An indicating device comprising anamplifier and voltmeter is connected between the collector and thereference potential.

In the drawings:

FIG. 1 is a diagrammatic view useful in explaining the operation of theinvention.

FIG. 2 is a perspective, with portions of the structure broken away, ofa modification of the embodiment illustrated diagrammatically in FIG. 1.

FIG. 3 is an elevation of an embodiment of the invention particularlyadapted for use as an automotive fuel gauge.

FIG. 4 is a sectional view taken along the line 4--4 of FIG. 3.

FIG. 5 is a sectional view taken along the line 5-5 of FIG. 4

FIG. 6 is a sectional view taken along the line 6-6 of FIG.

FIG. 7 is a sectional view taken along the line 7-7 of FIG.

FIG. 8 is a development of the outer conductive cylinder, or potentialplane, of FIG. 3 illustrating the application of a nonconductivesubstance thereto.

FIG. 9 is a simplified schematic and perspective of an embodiment of theinvention particularly suited for use in gauging lubricating oil level.

FIG. 10 is an elevation of the embodiment of FIG. 9.

- The gauge electrode elements are fabricated from sheet metal stock.Element 4 is the potential plane and is connected to terminal 3, whichprovides for connection to a source of electrical potential not shown.Element 5 is the reference element and is shown connected with container2 to the system ground 20. A potential difierence therefore existsbetween potential plane 4 and reference plane 5, which causes an ioniccurrent to flow in the portion of fluid 1 which is between conductiveelements 4 and 5. Interposed between elements 4 and 5 is element 6, thecollector. The collector is slantingly disposed between the other twoelements so that the distance between the potential plane and thecollector varies directly with depth and the distance between thereference plane and the collector varies inversely with depth. A currentflowing between the potential plane and the reference plane, thereforeflows through a first resistor comprising the fluid between thepotential plane and the collector and a second resistor comprising thefluid between the collector and the reference plane. The two saidresistances are electrically in series with each other. The collectorcomprises a tap at the junction of the two said resistances. Since theresistances are in series, the same current flows through each. Thepotential appearing at the collector is therefore a function of theratio of resistance of the two resistors. The resistance of eachresistor is a function of the conductivity of the fluid, thecross-sectional area of the current path, and the length of the currentpath. The cross-sectional area of the current paths of the two resistorsare equal and the effective electrical lengths of the current paths ofthe two resistors vary oppositely as the depth of fluid varies. Sincethe potential appearing at the collector is a function of the ratio ofthe resistances, this potential may be seen to be independent of theconductivity of the fluid provided only that the fluid conductivity beuniform. The potential appearing at collector 6 is transmitted byconductor 7 to an amplifier 8 whose output drives a voltmeter 9 which isconnected between the output of amplifier 8 and terminal 10 which isconnected to the reference potential. The voltmeter may be calibrated toindicate the volume or depth of fluid l in container 2 as desired.Collector 6 is shown as a flat sheet, which provides a logarithmic gaugefunction, however, linearity or any desired non-linearity of gaugefunction can be provided by bending the collector into a curved shape.It is, of course, also possible to affect the gauge function by controlof the amplifier function if desired. For example, with a flat collectoras shown in the drawing, an overall linear function for the gauge systemcould be had by designing the amplifier to exhibit an antilogarithmicfunction.

FIG. 2 illustrates another form of the inventive gauge struc ture. Here,the potential plane 11 and the reference plane 12 are formed as righttriangular conductive sheets and are joined along their respectivehypotenuses in a coplanar orientation by an insulating adhesive 15. Thecollector i3 is a rectangular conductive sheet which is disposedparallel to the plane of the potential plane and reference plane. Inthis form of the invention the lengths of the conductive paths of thetwo fluid resisters are equal and the ratio of the current carryingcrosssectional areas of the two resistors varies as the depth of fluidvaries. In all other respects the operation of the form of the inventionshown in FIG. 2 is the same as that of the form shown in FIG. 1.

FIG. 3 shows an embodiment of the invention which is particularlyadapted for use as an automotive fuel gauge. FIGS. 4 through 8illustrate features and details of construction of this embodiment.

The embodiment of FIG. 3, indicated generally by 30, is a fuel gaugetank element comprising three concentric cylindrical conductive tubes35, 36 and 34 which are mechanically, but not electrically, connected byplastic spacer 50 at one end to each other and to a mounting plate 3!adapted to depend the tubes into a fuel tank, not shown, through a holecut into the upper surface of said tank. The innermost conductive tube35 serves as the reference plane and is maintained at the automobilechassis ground potential. A screen-type fuel filter 25 is attached tothe assembly at the lower end of inner conduc- 5 tive tube 35 by plasticspacer 60 thereby adapting said inner conductive tube to use as the fuelfilling tube. The intermediate conductive tube 36 is the collector andis electrically connected to terminal 37 whereby it may be connected tothe remote indicating device. The outermost conductive tube 34 is thepotential plane and is electrically connected to terminal 33 whichprovides for connection to the high side of the automobile electricalsystem. Referring to FIG. 8 which shows a plane development of thecylindrical potential plane 34 of FIG. 3, the developed potential planeis indicated generally by 340 and its inner surface is being viewed. Theinner surface of the outermost tube is painted with non-conductive paint51 in a pattern determined by the desired gauge characteristic. Thisprovides that only the unpainted area 52 of the potential plane will beefiective in determining the current carrying cross-section of a firstresistor comprising the fuel between the potential plane 34 and thecollector 36. Therefore the ratio of resistance of said first resistorto the resistance of a second resistor comprising the fuel between thecollector 36 and the reference plane 35 of FIG. 3 varies proportionallyto the depth of fuel at the gauge elements.

The ratio of the resistances of these two fluid resistors isdeterminative of the voltage appearing at the collector. The actualvalue of the resistors is immaterial. In the absence of non-conductivepaint, therefore, the collector potential will be constant regardless ofthe fluid level. This is true because the resistance of each resistor isdetermined by the conductivity of the fluid, the length of the currentpath, and the conductive area of the current path. Mathematically:

R p I/A where R is the resistance, p is the reciprocal of theconductivity of the fluid,

A is the current carrying cross-sectional area, and I is the length ofthe current path. Since we are dealing with concentric cylindricalresistors:

and

where R is the resistance of the first fluid resistor comprising thefluid between reference plane 35 and collector 36, p is the reciprocalof the conductivity of the fluid comprising said first fluid resistor, Iis the length of the current path in said first fluid resistor, d, isthe mean effective diameter of the first fluid cylinder,

between electrodes 35 and 36 h is the height to which said firstcylinder contains fluid, R, is the resistance of the second fluidresistor comprising the fluid between potential plane 34 and collector36, p is the reciprocal of the conductivity of the fluid comprising saidsecond fluid resistor, 1 is the length of the current path in saidsecond fluid resistor, d,, is the mean efiective diameter of the secondfluid cylinder, between electrodes 34 and 36, h: is the height to whichsaid second cylinder contains fluid. Since uniform fluid conductivitywas assumed, p, p,. Since at any fluid level the height of the fluidresistor cylinders 70 is equal, h, h,. Therefore, the equations may besimplified:

R p lz/wligh.

The ratio of the resistors is:

- sistor, contacting one painted surface (34), is a higher orderfunction of fluid height. This leads to the mathematical conclusion:

where K is a constant, and

where flh) is a function describing the geometry of the non-conductivecoating.

The application of non-conductive paint, then, causes the resistanceratio to be a function of fluid height; said function is the gaugefunction and may be selected at the designer's option by design of thegeometry of the non-conductive coating. The potential at the collectoris thus indicative of the depth of fuel and may be measured by avoltmeter connected between terminal 37 and vehicle ground. The metermay be calibrated to read in terms of depth or volume of fuel asdesired. A linear or any desired non-linear gauge function, orcompensation for irregular fuel tank shape may be provided by selectionof the pattern in which the non-conductive coating is applied to thepotential plane. a

FIG. 4 shows conductive elements 34, 35 and 36 in end view, the mode ofattachment of the gauge elements to the supporting plate 31 by means offasteners 41, 42 and 43 comprising portions of the plastic spacermaterial which are ultrasonically staked over the periphery of holes inplate 31, terminals 33 and 37, their corresponding conductive tabs 33'and 37' which respectively connect terminal 33 to the potential plane 34and terminal 37 to the collector 36, and ground tab 45.

FIG. 5 is a sectional view of a portion of the fuel gauge taken'alongthe line 5-5 of FIG. 4. FIG. 5 shows in detail spacer block 50 which isof plastic material which has been molded about conductive plate 63after the terminals and contact strips have been punched therefrom. Thedepending gauge element assembly-is secured to spacer block 50 by adimple 61 in the potential plane 34. Terminal 33 is connected topotential plane 34 by connecting strip 33'. Terminal 33 and connectingstrip 33 comprise a single continuous conducting strip which has beenpunched from sheet 63. Said continuous conductive strip departs from theplane of the section in a roughly chordal arc in order to avoidelectrical contact with the reference plane 35.

FIG. 6 is a sectional view of a portion of the fuel gauge taken alongthe line 6-6 of FIG. 4. FIG. 6 particularly points out the connection ofcollector 36 to terminal 37 by connecting strip 37. This connection maybe constructed in the same way as the connection between potential plane34 and terminal 33 discussed above. Alternatively, strip 37' may beconnected to the input terminal of an integrated circuit amplifier whoseoutput terminal is connected to terminal 37.

FIG. 7 is a sectional view of the upper portion of the fuel gauge takenalong the line 7-7 of FIG. 4. This view points out particularly themethod whereby the gauge assembly is attached to mounting plate 31, thelocation of an integrated circuit amplifier within the gauge assembly,and the gauge grounding scheme. The gauge assembly is attached to themounting plate by first placing a resilient gasket 62 on the top surfaceof plastic spacer block 50. Spacer block 50 is so molded that a portionof the plastic material extends upwardly through a hole in gasket 62 anda corresponding hole in mounting plate 31; said plastic material is thenultrasonically staked over to form fastener 41. The automobile chassisground potential is conducted from the fuel tank to reference plane 35by mounting bracket 31. The ground potential is also conducted frombracket 31 to integrated circuit amplifier chip 70 by ground tab 45.Integrated circuit chip 70 is interconnected within the gauge structureto perform the function of amplifier 8 which was described withreference to FIG. 1. FIG. 7 shows the ground connection to amplifierchip 70. A similar connection between chip 70 and terminal 33 providesamplifier operating power. The amplifier input terminal is connected tocontact strip 37' and the amplifier output terminal is connected toterminal 37.

FIGS. 9, l0 and 11 illustrate an embodiment of the inventionparticularly adapted to use as an automotive lubricating oil low levelwarning system. FIG. 9 illustrates the principle of operation of thisembodiment. The automobile battery, shown schematically as 93, has itshot tenninal connected to a con ductive, cylindrical segment 94comprising the potential plane, and its ground side connected to asecond conductive cylindrical segment 95 which comprises the referenceplane. The two cylindrical segments are of equal radius and are disposedcoaxially with the lower edge of the potential plane cylinder a shortdistance above the upper edge of the reference plane cylinder. Thecollector 96 is a conductive rod which is disposed along the axis of thecylinders. Collector 96 is connected to an amplifier 98 which is in turnconnected to an indicating device comprising voltage responsive switch99a and indicator lamp 99b. When the crankcase is full both cylindricalsegments are completely immersed in and filled with oil and collector 96is at a potential determined by the relative volumes of the cylinders.When the oil level drops below the top of potential plane 94, theresistance of the oil encompassed by said potential plane increasesbecause the current carrying cross-sectional area of the oil decreases.This produces a change in the potential of collector 96. When thepotential of collector 96 reaches a predetermined level, correspondingto an undesirably low oil level, voltage responsive switch 99a isactuated causing indicator lamp 99b to light.

FIG. 10 shows an oil level warning device embodying the presentinvention which is constructed integrally with the oil pan drain plug. Abolt 101 having lower threaded portion 102 mechanically secures theelements of the device in cooperation with nut 103 and provides aportion of the electrical conduction path between the automobile batteryand potential plane 106. A wire from the hot side of the battery notshown is connected to the bolt at 102 and is securely clamped betweennuts 103 and 104. Electrical contact between bolt 101 and the remainderof the device is prevented by plastic insulator 105. Reference plane 107includes a threaded portion 107a threaded to engage the threads of theoil] pan drain hole, and hexagonal nut portion 107b whereby the devicemay be inserted into and removed from the oil pan. Electrical connectionof reference plane 107 to the automobile ground is accomplished bydirect contact to the oil pan at 107a. The amplifier shown at 98 in FIG.9 may, if desired, be an integrated circuit amplifier located in ahollowed volume in hex nut member 107b.

In the FIG. 10 embodiment oil communicates between the crankcase and thegauge through the gap between potential plane 106 and reference plane107. The top surface of potential plane 106 has a plurality of ventholes which prevent an air bubble from becoming trapped within thepotential plane structure.

If a continuous reading oil level gauge is desired rather than a lowlevel warning, it is considered an obvious alternative within the scopeof this invention to increase the height of potential plane 106 so thatit extends to the maximum height of oil in the crankcase, and to replacevoltage responsive switch 99a and lamp 99b of FIG. 9 with anappropriately calibrated voltmeter.

FIG. 11 is a longitudinal sectional view of a minor variant of the gaugeof FIG. 10. The variation from the FIG. 10 embodiment consists ofmechanically closing the gap between potential plane 106 and referenceplane 107 with a ring of insulating material 111, providing a pluralityof holes 113 in the lower portion of reference plane 107, and includingfibrous filter material 112 within the gauge structure wherebymechanical resistance to the flow of oil in and out of the gaugestructure is provided. The purpose of these variations is to damp anysloshing of the oil within the gauge which might occur as a result ofvehicular motion. All other features shown in FIG. 11 are also presentin the FIG. 10 embodiment.

Collector 108 is positioned and insulated within the structure byplastic spacer 116. Additional electrical insulation is provided betweenbolt 101 and collector 108 by insulating material 117. Bolt 101 is inelectrical contact with potential plane 106. Vent holes 1 15 areprovided in the upper surface of potential plane 106.

The invention claimed is:

1. A floatless fluid level gauge for gauging fluid comprising:

a pair of electrodes comprising first and second electrodes immersed insaid fluid;

means for maintaining a potential difference between said first andsecond electrodes;

a third electrode immersed in said fluid and disposed in the currentpath between said first and second electrodes, said first, second andthird electrodes being so configured that the ratio of the resistancethrough said current path in said fluid between said first and thirdelectrodes with respect to the resistance through said current path insaid fluid between said second and third electrodes has a generallyunique value for each depth of immersion of said electrodes in saidfluid; and means for sensing the potential of said third electrode,wherein said pair of electrodes comprise two conductive sheetsnon-conductively joined along an edge of each to form a unitary sheetand said third electrode is a conductive sheet disposed in spacedrelationship to said pair of electrodes.

2. The gauge of claim 1 wherein said conductive sheets are planar inform.

3. A floatless fluid level gauge for gauging fluid comprising:

a pair of electrodes comprising first and second electrodes immersed insaid fluid;

means for maintaining a potential difference between said first andsecond electrodes;

a third electrode immersed in said fluid and disposed in the currentpath between said first and second electrodes, said first, second andthird electrodes being so configured that the ratio of the resistancethrough said current path in said fluid between said first and thirdelectrodes with respect to the resistance through said current path insaid fluid between said second and third electrodes has a generallyunique value for each depth of immersion of said electrodes in saidfluid; and means for sensing the potential of said third electrode,wherein said pair of electrodes comprise two congruent right triangularconductive sheets non-conductively joined along their hypotenuses toform a rectangular sheet and said third electrode is a rectangularconductive sheet disposed in spaced relationship to said pair ofelectrodes.

4. The gauge of claim 3 wherein said third electrode is disposed in aplane parallel to the plane of the first mentioned rectangular sheet.

5. A floatless fluid level gauge for gauging fluid comprising:

a pair of electrodes comprising first and second electrodes immersed insaid fluid;

means for maintaining a potential difference between said first andsecond electrodes;

a third electrode immersed in said fluid and disposed in the currentpath between said first and second electrodes, said first, second andthird electrodes being so configured that the ratio of the resistancethrough said current path in said fluid between said first and thirdelectrodes with respect to the resistance through said current path insaid fluid between said second and third electrodes has a generallyunique value for each depth of immersion of said electrodes in saidfluid; and means for sensing the potential of said third electrode,wherein said pair of electrodes comprise two conductive tubes of similarcrosssection disposed one above the other and said third electrode is anelongated conductive body disposed within said tubes.

6. A floatless fluid level gauge for gauging fluid comprising:

a pair of electrodes comprising first and second electrodes immersed insaid fluid;

means for maintaining a potential diflerence between said first andsecond electrodes;

a third electrode immersed in said fluid and disposed in the currentpath between said first and second electrodes, said first, second andthird electrodes being so configured that the ratio of the resistancethrough said current path in said fluid between said first and thirdelectrodes with respect to the resistance through said current path insaid fluid between said second and third electrodes has a generallyunique value for each depth of immersion of said electrodes in saidfluid; and means for sensing the potential of said third electrode,wherein said pair of electrodes comprise two right cylindrical segmentshaving similar cross-sections and disposed coaxially one above theother, and said third electrode is disposed within said rightcylindrical segments parallel to the axis thereof and generallycoextensive therewith.

7. The gauge of claim 6 wherein said right cylindrical segments are ofequal height.

8. The gauge of claim 6 wherein said third electrode is a third rightcylindrical segment disposed within said two right cylindrical segments.

9. The gauge of claim 6 wherein one of said two cylindrical segments isthreaded over a portion of its outer surface, and with additionally, abase member closing one end of said one segment.

10. The gauge of claim 9 wherein said base member is shaped forengagement by a wrench.

11. The gauge of claim 9 wherein said base member has a hollowed portiontherein and wherein said gauge additionally includes means for sensingthe potential of said third electrode comprising an integrated circuitdevice disposed within said hollowed portion of said base member.

12. The gauge of claim 9, with additionally, fibrous filter means fordamping the movement of fluid within said gauge.

13. The gauge of claim 9 wherein said means for sensing comprisesvoltmeter means responsive to the potential appearing on said thirdelectrode.

14. The gauge of claim 9 wherein said means for sensing potentialcomprises:

potential responsive switching means connected to said third electrode;and,

indicator means controlled by said switching means.

15. A floatless fluid level gauge comprising:

three electrodes immersed in the fluid to be gauged, said electrodesbeing so configured that the ratio of the volume of said fluid between afirst and third of said electrodes with respect to the volume of saidfluid between said third and a second of said electrodes has a generallyunique value for each depth of immersion of said electrodes in saidfluid;

means for maintaining a potential difference between two of saidelectrodes, whereby an electric current is caused to flow between saidtwo electrodes, the other of said electrodes being disposed in thecurrent path between said two electrodes; and,

means for sensing the potential of said third electrode, wherein saidfirst and second electrodes comprise two right cylindrical segments ofunequal cross-section disposed coaxially one within the other, and saidthird electrode is a right cylindrical segment of cross-sectionintermediate to the cross-sections of the electrodes of the other twoelectrodes.

16. The gauge of claim including additionally a non-conductive coatingapplied to one surface of one of said other two electrodes whereby theeffective conductive area of said coated electrode is caused to vary asa non-linear function of the level to which fluid contacts said coatedelectrode.

17. The gauge of claim 16 wherein said coated electrode is the outermostof said cylindrical segments and said coated surface is the innersurface thereof, and the innermost of said cylindrical segments ismaintained at said reference potential and includes additionally afiltering screen at the lower end thereof whereby said innermostcylindrical segment is adapted to be used for filling a container withthe fluid to be gauged.

18. The gauge of claim 15 including additionally a mounting

1. A floatless fluid level gauge for gauging fluid comprising: a pair ofelectrodes comprising first and second electrodes immersed in saidfluid; means for maintaining a potential difference between said firstand second electrodes; a third electrode immersed in said fluid anddisposed in the current path between said first and second electrodes,said first, second and third electrodes being so configured that theratio of the resistance through said current path in said fluid betweensaid first and third electrodes with respect to the resistance throughsaid current path in said fluid between said second and third electrodeshas a generally unique value for each depth of immersion of saidelectrodes in said fluid; and means for sensing the potential of saidthird electrode, wherein said pair of electrodes comprise two conductivesheets non-conductively joined along an edge of each to form a unitarysheet and said third electrode is a conductive sheet disposed in spacedrelatioNship to said pair of electrodes.
 2. The gauge of claim 1 whereinsaid conductive sheets are planar in form.
 3. A floatless fluid levelgauge for gauging fluid comprising: a pair of electrodes comprisingfirst and second electrodes immersed in said fluid; means formaintaining a potential difference between said first and secondelectrodes; a third electrode immersed in said fluid and disposed in thecurrent path between said first and second electrodes, said first,second and third electrodes being so configured that the ratio of theresistance through said current path in said fluid between said firstand third electrodes with respect to the resistance through said currentpath in said fluid between said second and third electrodes has agenerally unique value for each depth of immersion of said electrodes insaid fluid; and means for sensing the potential of said third electrode,wherein said pair of electrodes comprise two congruent right triangularconductive sheets non-conductively joined along their hypotenuses toform a rectangular sheet and said third electrode is a rectangularconductive sheet disposed in spaced relationship to said pair ofelectrodes.
 4. The gauge of claim 3 wherein said third electrode isdisposed in a plane parallel to the plane of the first mentionedrectangular sheet.
 5. A floatless fluid level gauge for gauging fluidcomprising: a pair of electrodes comprising first and second electrodesimmersed in said fluid; means for maintaining a potential differencebetween said first and second electrodes; a third electrode immersed insaid fluid and disposed in the current path between said first andsecond electrodes, said first, second and third electrodes being soconfigured that the ratio of the resistance through said current path insaid fluid between said first and third electrodes with respect to theresistance through said current path in said fluid between said secondand third electrodes has a generally unique value for each depth ofimmersion of said electrodes in said fluid; and means for sensing thepotential of said third electrode, wherein said pair of electrodescomprise two conductive tubes of similar cross-section disposed oneabove the other and said third electrode is an elongated conductive bodydisposed within said tubes.
 6. A floatless fluid level gauge for gaugingfluid comprising: a pair of electrodes comprising first and secondelectrodes immersed in said fluid; means for maintaining a potentialdifference between said first and second electrodes; a third electrodeimmersed in said fluid and disposed in the current path between saidfirst and second electrodes, said first, second and third electrodesbeing so configured that the ratio of the resistance through saidcurrent path in said fluid between said first and third electrodes withrespect to the resistance through said current path in said fluidbetween said second and third electrodes has a generally unique valuefor each depth of immersion of said electrodes in said fluid; and meansfor sensing the potential of said third electrode, wherein said pair ofelectrodes comprise two right cylindrical segments having similarcross-sections and disposed coaxially one above the other, and saidthird electrode is disposed within said right cylindrical segmentsparallel to the axis thereof and generally coextensive therewith.
 7. Thegauge of claim 6 wherein said right cylindrical segments are of equalheight.
 8. The gauge of claim 6 wherein said third electrode is a thirdright cylindrical segment disposed within said two right cylindricalsegments.
 9. The gauge of claim 6 wherein one of said two cylindricalsegments is threaded over a portion of its outer surface, and withadditionally, a base member closing one end of said one segment.
 10. Thegauge of claim 9 wherein said base member is shaped for engagement by awrench.
 11. The gauge of claim 9 wherein said base member has a hollowedportion therein and wherein saiD gauge additionally includes means forsensing the potential of said third electrode comprising an integratedcircuit device disposed within said hollowed portion of said basemember.
 12. The gauge of claim 9, with additionally, fibrous filtermeans for damping the movement of fluid within said gauge.
 13. The gaugeof claim 9 wherein said means for sensing comprises voltmeter meansresponsive to the potential appearing on said third electrode.
 14. Thegauge of claim 9 wherein said means for sensing potential comprises:potential responsive switching means connected to said third electrode;and, indicator means controlled by said switching means.
 15. A floatlessfluid level gauge comprising: three electrodes immersed in the fluid tobe gauged, said electrodes being so configured that the ratio of thevolume of said fluid between a first and third of said electrodes withrespect to the volume of said fluid between said third and a second ofsaid electrodes has a generally unique value for each depth of immersionof said electrodes in said fluid; means for maintaining a potentialdifference between two of said electrodes, whereby an electric currentis caused to flow between said two electrodes, the other of saidelectrodes being disposed in the current path between said twoelectrodes; and, means for sensing the potential of said thirdelectrode, wherein said first and second electrodes comprise two rightcylindrical segments of unequal cross-section disposed coaxially onewithin the other, and said third electrode is a right cylindricalsegment of cross-section intermediate to the cross-sections of theelectrodes of the other two electrodes.
 16. The gauge of claim 15including additionally a non-conductive coating applied to one surfaceof one of said other two electrodes whereby the effective conductivearea of said coated electrode is caused to vary as a non-linear functionof the level to which fluid contacts said coated electrode.
 17. Thegauge of claim 16 wherein said coated electrode is the outermost of saidcylindrical segments and said coated surface is the inner surfacethereof, and the innermost of said cylindrical segments is maintained atsaid reference potential and includes additionally a filtering screen atthe lower end thereof whereby said innermost cylindrical segment isadapted to be used for filling a container with the fluid to be gauged.18. The gauge of claim 15 including additionally a mounting plate and aplastic spacer block attached thereto for supporting said electrodes inthe fluid to be gauged.
 19. The gauge of claim 18 wherein said means forsensing potential comprises: utilization means responsive to saidpotential at said third electrode; and, means connecting said thirdelectrode to said utilization means.
 20. The gauge of claim 19 whereinsaid means for connecting comprises an integrated circuit devicedisposed within said plastic spacer block.